This invention relates to apparatus for frying foods and particularly to improved deep fat fryers wherein fat or oil heated externally of the fryer vessel or tank is recirculated therethrough. The invention is discussed in and was developed in conjunction with the fryer invention of U.S. Pat. No. 4,487,691 issued to Robert Panora on Dec. 11, 1984, which patent is incorporated herein by reference.
Deep fat frying of foods such as potatoes, fish, meats, and pastries is performed by immersing the foods in a tank containing heated cooking oil or fat. Of considerable importance in such fryers are their systems for heating the fat and for maintaining its temperature uniformity and cleanliness.
Of as great importance is the fryer's productivity, not only during actual frying operation, but also in enabling quick start-up at the beginning of the day or whenever the unit has fat replaced during the day, particularly if more economical solid shortening (rather than liquid oil) is used. This invention was specifically designed for the pumped fat recirculation, external heat exchanger-type fryer illustrated in the aforementioned U.S. Pat. No. 4,487,691.
Several potential problems exist in a pump recirculation unit of the type disclosed herein. First, it is near impossible to prevent water or steam from causing pump vapor lock and reduced or possibly inhibited flow of the heated fat when that occurs. Reduced flow means slower heat recovery, potential scorching of the fat while in the firing range of the burner and possible damage to the heat exchanger, among other things. If recirculation is slowed or stopped while the thermostat in the tank continues to call for more heat, poor frying results or damage can occur. The present invention solves the problem by a unique method and apparatus of sensing reduced fat flow or pressure, releasing the vapor lock if it occurs, and restarting the circulating system upon release. Second, a fryer of the type disclosed has difficulty enabling use of typically lower-cost solid shortening instead of liquid oil. Existing deep fat fryers have burner heat applied directly to the tank bottom and side walls. While they can melt solid shortening fairly rapidly, the fat is sometimes subject to scorching, resulting in shorter fat life and adversely affecting food taste. Since the heat exchanger of a fryer embodying the present invention is essentially "remote" from the tank in the sense that it need not be against the tank walls, typical solutions to the problem are that solid shortening should either be heated in pans on a stove and poured into the fryer (with the potential personal danger accompanying the handling of hot fat), or more expensive liquid fat or oil should be used. Although the heat exchanger of the design illustrated is preferably conveniently below the tank, its efficiency to heat the tank bottom for melting solid shortening is somewhat restricted. Furthermore, if sufficient heat is applied to the tank bottom, the heat exchanger may be subjected to excessive heat and resultant damage and potential leakage. The present invention solves that problem by the unique apparatus which may be the same or a separate apparatus from that used to eliminate the vapor lock. The method for performing the melting of solid shortening is one which is convenient and relatively fast, while protecting both the fat and the equipment from damage.
To solve both the pump vapor lock problem and enable the capability of melting solid shortening in a fryer of the type disclosed, automatic controls are provided to operate a pump motor and burner continuously or intermittently in response to a condition indicating lack of flow in the tubing or piping between the pump impeller and heat exchanger. Preferably, pressure is sensed to indicate absence or reduction of the flow and the unit is automatically controlled in response to the existence or nonexistence of a predetermined pressure.